An angioplastic technique employing balloon catheters is known in the art. Such a technique involves threading a catheter arrangement, including a thin guide wire (which may have a diameter of only about 20 mils) and a deflated balloon located toward the distal end of the catheter, through the vascular system of a patient's body until the balloon is situated within the bore of the lumen of a vas, such as a coronary artery, that is partially occluded with atherosclerotic plaque. The balloon is then inflated with a liquid, which causes the inflated balloon to press against the plaque (which is usually comprised of a fatty substance, but which may to some extent be calcified). In any case, the pressure of the inflated balloon against the plaque of the partially occluded lumen deforms the plaque and the walls of the vas, thereby enlarging the bore of the lumen.
It has been found that the fatty substance of the plaque may be softened and that the walls of the vas may be stiffened by heating the plaque to a given temperature. While this given temperature has to be sufficiently high to result in the desired softening and stiffening, it must not become so high as to unduly injure the underlying tissue of the vas. In this regard, reference is made to U.S. Pat. No. 4,643,186, which issued to Rosen et al. on Feb. 17, 1987. This Rosen et al. patent discloses the use of microwave energy to provide the desired heating of the plaque and the walls of the vas. The microwave energy is radiated from an antenna situated toward the distal end of the catheter. The radiated microwave energy may directly dielectrically heat the plaque and the walls of the vas and/or the radiated microwave energy may dielectrically heat the liquid inflating the balloon which, in turn, heats the plaque and the walls of the vas by conduction of heat therefrom through the balloon.
Further, it has been found that a portion of the fatty substance of the plaque under such heat and pressure tends to liquify and rise to the surface of the plaque. In this regard, reference is made to my allowed U.S. patent application Ser. No. 07/190,179, filed May 4, 1988. This application discloses sucking out, through the catheter, the liquified fatty substance of the plaque produced by the pressure thereagainst by an inflated balloon and the direct and/or indirect heating thereof by radiated energy from an antenna situated toward the distal end or the catheter.
There are problems associated with heating the plaque by means of radiated energy from an antenna situated toward the distal end of a balloon catheter. Such a catheter requires a transmission line extending the length of the catheter for energizing the antenna. Further, in order to avoid undue injury to the underlying vas tissue by overheating beyond a safe desired temperature, a temperature sensing element must also be situated toward the distal end of the catheter, and the output of such temperature sensing element must be transmitted to an energy control device situated outside of the patient's body by means of wires extending the length of the catheter. The presence of the antenna, transmission line, temperature sensing element and wires limits the minimum size of the diameter of the catheter. Therefore, such a catheter cannot be inserted into small veins or arteries or into a larger vas in which the thickness of the plaque occluding the lumen thereof is so great to make the original bore of this occluded lumen too small to fit the diameter of the catheter. Furthermore, no type of balloon catheter can be used to open or enlarge a completely or a substantially completely occluded lumen of a vas.